V4L2 compound read-only custom control
 

Hi,

I have a camera V4L2 driver. Now I want to add the possibility to query the chip's global unique identification. This information is split into 3 registers (each 16 bit). I ended up with a new custom read-only control:
struct cam_ident {
u16 efuseval2;
u16 efuseval3;
u16 efuseval4;
};

The control is configured like this:
.ops = &cam_ctrl_ops,
.id = CAM_CID_IDENT,
.name = "Get ident information",
.type = V4L2_CTRL_COMPOUND_TYPES,
.flags = V4L2_CTRL_FLAG_HAS_PAYLOAD | V4L2_CTRL_FLAG_READ_ONLY,
.min = S32_MIN,
.max = S32_MAX,
.step = 1,
.def = 0,
.elem_size = sizeof(struct cam_ident),
.dims = {1}

1. Question:
Is this the right way to model the identfication?
2. Question:
How can I set the control's value from the kernel side?
I know that there are helper functions like v4l2_ctrl_s_ctrl or v4l2_ctrl_s_ctrl_string (taken from https://www.kernel.org/doc/html/v4.1...-controls.html), but they can't set a compound control.
I also tried setting ctrl->p_new->p and ctrl->p_cur->p also without success.

How about /sys /proc?